Method for producing bubble domains in magnetic film-substrate structures

ABSTRACT

A METHOD FOR PRODUCING A BUBBLE DOMAIN IN AMAGNETIC SINGLE CRYSTLA GARNET FILM-SUBSTRATE STRUCTURE IS DISCLOSED. THE METHOD INVOLVES THE EPTIAXIAL DEPOSITION OF AN IRON GARNET FILM OF THE PROPER ORIENTATION AND HAVING A NEGATIVE MAGNETOSTRICTION CONSTANT ON A GARNET SUBSTRATE IN WHICH THE ROOM TEMPERATURE LATTICE CONTHE FILM IS LARGER THAN THE ROOM TEMPERATURE LATTICE CONSTANT OF THE SUBSTRATE BY AN AMOUNT GREATER THAN ABOUT 0.035 ANGATROM.   D R A W I N G

Jan. 29, 1974 J. E. MEE ETAL INVENTORS JACK E. MEE BY PAUL J. BESSER ATTORNEY United States Patent 3,788,896 METHOD FOR PRODUCING BUBBLE DOMAINS IN MAGNETIC FILM-SUBSTRATE STRUCTURES Jack E. Mee, Anaheim, and Paul J. Besser, Mission Viejo,

Califi, assignors to North American Rockwell Corporation, El Segundo, Calif.

Filed Dec. 28, 1970, Ser. No. 101,787 Int. Cl. H01f 10/06 U.S. Cl. 117-235 5 Claims ABSTRACT OF THE DISCLOSURE A method for producing a bubble domain in a magnetic single crystal garnet film-substrate structure is disclosed. The method involves the epitaxial deposition of an iron garnet film of the proper orientation and having a negative magnetostriction constant on a garnet substrate in which the room temperature lattice constant of the film is larger than the room temperature lattice con stant of the substrate by an amount greater than about 0.035 angstrom.

The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 U.S.C. 2457).

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to bubble domains and more particularly to a method of forming a film having bubble domains therein.

(2) Description of prior art Magnetic bubble domains in a sheet of magnetic medium, such as yttrium orthoferrite, are well known in the art and are described in U.S. Pat. No. 3,460,116 and others. Magnetic bubble domains in composite structures having a thin film of a single crystal iron garnet on an oxide substrate are disclosed in the co-pending patent applications to Mee et al., U.S. Ser. Nos. 16,446 filed Mar. 4, 1970 and now U.S. Pat. No. 3,645,788, and 16,447, filed Mar. 4, 1970. These co-pending patent applications are incorporated herewith.

Some iron garnet film-substrate structures were observed to have domains whose magnetization directions are in the plane of the film in. contrast to the desired bubble domains whose magnetization directions are perpendicular to the plane of the film.

SUMMARY OF THE INVENTION It is a primary object of this invention to provide an improved method of forming a single crystal iron garnet film-substrate structure having bubble domains therein.

This and other objects of this invention are accomplished by a method in which the uniaxial anisotropy necessary for bubble domain formation in film-substrate structure is affected by proper control of the mechanical stress present in the film at room temperature. A specific step in the method involves depositing a single crystal iron garnet film of the proper crystallographic orientation and having a negative magnetostriction constant on a substrate in which the room temperaturelattice constant of the film is larger than the room temperature lattice con- 3,788,896 Patented Jan. 29, 1974 apparent from the following detailed description wherein a preferred embodiment of the present invention is clearly shown.

BRIEF DESCRIPTION OF THE DRAWING The drawing shows a magnetic bubble domain filmsubstrate structure made in accordance with the method of this invention.

DETAILED DESCRIPTION OF THE INVENTION This invention involves a process in which a single crystal iron garnet material is chemically vapor deposited to form a film on a substrate. It is necessary that the single crystal material have the proper crystallographic orientation to take advantage of the negative magnetostriction. In addition the room lattice constant of the deposited film is larger than the room lattice constant of the substrate by an amount greater than about 0.035 angstrom. The resultant film-substrate structure has a craze-free film with bubble domains therein.

In general, the normal source of uniaxial anisotropy observed in magnetic material is the crystal structure of the material. When single crystal platelets with negative magnetostriction constants (A A 0), are under stress the magnetostriction contribution tends to make the normal to the plane of the platelet an easy axis of magnetization if the platelet is in tension, (o' 0), and a hard axis if the platelet is in compression, (o' 0) where A and M are the saturation valves of the linear magnetostriction constants along the 100 and 111 directions, respectively, and 0' is the stress in the plane of the material.

The room temperature magnetostriction constants of selected iron garnets are listed in the following table.

Magnetostriction constant Iron garnet Moo (X10 Mn (X The values of the magnetostriction constants of the iron garnet material, as well as its magnetization, can be varied by depositing a film containing a mixture of two or more pure iron garnets and/ or by substituting other cations for iron ions.

It is understood that whether there is mixing and/or substitution or not, the condition for bubble domain formation in the iron garnet material, H /41rM 1, has to be satisfied, where H is the uniaxial anisotropy field and 41rM is the magnetization.

In magnetic oxide film-substrate structures formed by chemical vapor deposition, the dominant source of uniaxial anisotropy is the magnetostrictive efiect resulting from the stress existing in the film. This stress is due to the difference between the lattice constants and the thermal expansion coefiicients of the film and substrate and may be in the form of tension or compression.

This invention specifically covers a method of forming a bubble domain structure by depositing a magnetic single crystal garnet film of the proper orientation and having a negative magnetostriction constant on a substrate in which the film is in tension.

A co-pending application to Mee et al., Ser. No. 101,785 filed Dec. 28, 1970, covers a method of forming a bubble domain structure by depositing a magnetic single crystal garnet film of the proper orientation and having a positive magnetostriction constant on a substrate in which the film is in compression.

A co-pending application to Mee et al., Ser. No. 101,786 filed Dec. 28, 1970, covers a second method of forming a bubble domain structure by depositing a magnetic single crystal garnet film of the proper orientation and having a negative magnetostriction constant on a substrate in which the film is in tension.

As shown in the drawing, an oxide substrate is preferably subjected to a chemical vapor deposition step to provide a thin film of magnetic bubble domain material, film 12. The deposition step is carried out in accordance with the co-pending application, Ser. No. 833,268 filed June 16, 1969 and now abandoned, and assigned to the assignee of the present invention. This pending patent application is incorporated herewith by reference hereto.

neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, lanthanum and yttrium; the Q constituent of the film formulation is taken from the group consisting of iron, iron and aluminum, iron and gallium, iron and indium, iron and scandium, iron and titalium, iron and vanadium, iron and chromium, and iron and manganese.

The valence of the I constituent and the valence of the Q constituent add up to the same valence total as the oxide constituent. A preferred substrate material is samarium gallium garnet when the film material is gadolinium iron garnet.

In accordance with this invention, an iron garnet film of the proper orientation and having a negative magnetostriction constant is deposited on a garnet substrate in which the room temperature lattice constant of the film is larger than the room temperature lattice constant of the substrate by an amount greater than about 0.035 angstrom. When the film lattice constant exceeds the substrate lattice constant by an amount greater than about 0.035 angstrom the film is in tension and bubble domains are present therein. When the film lattice constant is larger than the substrate lattice constant by an amount less than about 0.035 angstrom, the film is in compression and there are no bubble domains since the normal to plane of the film is the hard axis and the domain magnetizations lie in the plane.

As previously discussed, the difference in the coefficients of thermal expansion between the fihn and the substrate contributes to total stress present in the film. The thermal expansion stress contribution is within acceptable limits as long as the coefiicient of thermal expansion of the substrate is the same as or lower than that of the film by an amount not more than 1X10-/ C. A certain amount of mismatch between film-substrate room temperature lattice constants and/or thermal expansion characteristics is required in order to provide the stress which produces the uniaxial anisotropy necessary for bubble domain formation. It film and substrate are too closely matched in both lattice constant and thermal expansion, the proper stress necessary for bubble domain formation will not be achieved.

or by a liquid phase epitaxial process.

The substrate 10 is monocrystalline garnet having a I Q O formulation wherein the J constituent of the wafer formulation is at least one element selected from the group consisting of cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, lanthanum, yttrium, calcium, and bismuth and the Q constituent of the wafer formulation is at least one element selected from the group consisting of indium, gallium, scandium, titanium, vanadium, chromium, manganese, rhodium, zirconium, hafnium, molybdenum, tungsten, niobium, tantalum, aluminum, phosphorus, arsenic and antimony.

Examples of substrate materials are samarium gallium garnet, and yttrium aluminum garnet.

The film of the bubble domain material is a single crystal garnet film having a J Q 0 formulation wherein the J constituent of the film formulation has at least one element selected from the group of cerium, praseodymium,

TABLE Substratm Film Substrate lattice constant Lattice Lattice minus film Orienconstant,- Orienconstant,- lattice Bubble Domains iEx. No. Material tion A. Substrate tation A. constant-,A. domain in-plane Stress I GdaFefiolfl (111) 12.471 SmsGasOn (111) 12.436 -0.035 IL YgGa -gFeg-gon 12.357 YgAlsOn (110) 12.010 0.347 III YaGar-zFea-sou (111) 12.357 'IbsGasOu (111) 12.347 -0.0l0 IV YsGai-zFea-son (111) 12.357 DyaGasou (111) 12.341 0.0l6 N0 At room temperature. The film 12 may also be deposited by sputtering techniques 55 We claim:

1. A method of producing a bubble domain containing film-substrate structure comprising the step of depositing a magnetic film of a single crystal material of the proper orientation and having a negative magnetostriction constant on a substrate in which the magnetic film has a room temperature lattice constant which exceeds the room temperature lattice constant of the substrate by an amount greater than about 0.035 angstrom.

2. A method of producing a bubble domain containing film-substrate structure comprising the step of depositing an iron garnet film of the proper orientation and having a negative magnetostriction constant on a substrate in which the iron garnet film has a room temperature lattice constant which exceeds the room temperature lattice constant of the substrate by an amount greater than about 0.035 angstrom.

3. A method as described in claim 2 whereby said film is deposited by a chemical vapor deposition technique.

4. A method of producing a bubble domain containing film-substrate structure comprising the step of depositing angstrom.

5. A method as described in claim 4 whereby said substrate is a samarium gallium garnet.

References Cited UNITED STATES PATENTS Mee et al. 117--240 Mee et al. 117--240 Hanak 117-235 Archey 117107 X 6 12/1969 Linares 117-235 X 2/1969 Mee 117-235 X 4/1964 Gambino 117235 3/1971 Moore et a1. 117-235 X OTHER REFERENCES Giess et al., IBM Tech. Dis. Bull., pp. 517, 117-235, vol. 13, N0. 2, July 1970.

10 WILLIAM D. MARTIN, Primary Examiner B. D. PIANALTO, Assistant Examiner US. Cl. X.R.

15 117106' R; 340-174 TF, 174 M UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,' 3a788896 Dated January 29, 1974 Jack E. Mee et a1. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters-Patent are hereby corrected as shown below:

change "b -1.4" and C01 2 1' 56 ft Y G v umn lne a er 3 a Fe O "b l.7" to -l.4 and 1.7 Column 4-,- line 6,

change "titalium" to titanium Signed and sealed this "17th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN v Commissioner of Patents Attesting Officer USCOMM-DC 6O376-P69 us. GOVERNMENT PRINTING OFFICE I969 os66-s34.

F ORM PO-1OSO (10-69) 

